GB2074380A

GB2074380A - A fault current circuit breaker

Info

Publication number: GB2074380A
Application number: GB8031974A
Authority: GB
Original assignee: Felten and Guilleaume Austria AG
Current assignee: Felten and Guilleaume Austria AG
Priority date: 1980-04-16
Filing date: 1980-10-03
Publication date: 1981-10-28
Also published as: DE3040244A1; AU542724B2; FR2480998B1; FR2480998A1; AU8238882A; BE888442A; NL8007025A; ATA204580A; AT372549B

Abstract

A fault current circuit breaker has a switching mechanism (5) with a fault current tripping device (1) comprise a yoke body (4) built up from spaced parallel layers of a ferromagnetic material separated by a non-ferromagnetic material or air. The layers of the body (4) are bridged by a permanent magnet (2) and a tripping armature (3) and the body (4) is provided with an opening (4A) which is arranged so that, at the area where the tripping armature (3) bears, the yoke cross section is less than that in the remainder of the yoke and the flux path is continuous and without an air gap in the layers around the opening (4A). The main current paths (L1, L2, L3 N) of the circuit breaker are guided through the opening (4A) in the yoke body (4) of the fault current tripping device (1) <IMAGE>

Description

SPECIFICATION A fault current circuit breaker The present invention relates to a fault current circuit breaker comprising a switching mechanism with a fault current tripping device.

In the case where such a circuit breaker comprises a contact arrangement, a testing device, and connecting terminals, the fault current tripping device usually comprises a yoke body built up from ferromagnetic layers extending parallel to each other and separated by a non-ferromagnetic material or air. The layers of the body are bridged by a permanent magnet and a tripping armature and the body comprises an opening or yoke window, which is arranged so that at the area where the tripping armature bears, the cross section of the yoke is greatly reduced for a magnetic flux which is continuous and without an air gap in the layers around the opening.

Fault current circuit breaker with permanent magnet tripping devices have already been frequently used, but an excitation winding was always provided in the yoke window, which winding was supplied by the secondary winding of a summation transformer. Fault current circuit breakers of this type were provided for protecting installations which are operated by alternating voltage, from insulation faults. In the prior art at that time, when an insulation fault occurred, one had only to deal with pure alternating fault currents in these installation, apart from a few exceptional cases, such as for example when protecting installations in which cathodic corrosion protection was used or in railways, i.e. in cases where one had to contend with pure D.C current flowing through the fault current circuit breakers.

In recent years, this situation has changed in so far that due to the use of semi-conductor components for electronic controls, more and more operating means are used in which when an insulation fault occurs. Fault currents with D.C. components flow to earth and thus the function of the fault current circuit breakers currently on the market is destroyed.

Therefore, accidents have not yet been reported because it is very improbable that the nesessary requirements will be met. However, the technology of fault current circuit breakers must nevertheless take into account the changed conditions in electrical installations and fault current circuit breakers must be developed which also operate in the case of D.C. fault currents. If one checks the possibilities of faults in electrically controlled operating means, then one finds that most fault currents which flow are in the form of pulsating half-wave currents. Above all, in the case of single-wave rectifications with smoothing capacitors and in the case of three-phase rectifications, if there is a fault, a smoothed direct current flows to earth.However,. a more thorough inspection of the development of a fault shows that this D.C. fault current generally occurs suddenly, so that fault current circuit breakers which are tripped in the case of pulsating half-wave currents and in the case of smoothed direct currents ocurring suddenly, irrespective of their direction, correspond to virtually all requirements as regards protection with normal use of electricity. Thus the D.C. fault current which increases slowly may be considered as the last problem to which a solution must still be sought.

The first of the above described tasks, namely of developing fault current circuit breakers which are tripped in the case of pulsating half-wave currents, can be solved if one uses a material for the summation transformer, which has low remanence, whereby in order to increase the tripping sensitivity, a capacitor is sometimes incorporated in the tripping circuit or with a tertiary winding of the summation transformer. Solutions of this type have already been described for example in Austrian Patent Specification No. 318052, German Auslegschrift No. 2811064 and Austrian Patent Application AZ 433/79. It is common to all these solutions that they use a summation transformer, i.e. they cannot operate in the case of D.C. fault currents which increase slowly.

However, if one uses non-polarized tripping devices, such as are described in Austrian Patent Specifications Nos. 242 777, 278954, 337811 and 337 812, i.e. tripping devices which operate irrespective of the direction of the fault current in the excitation winding, then a fault current circuit breaker according to the present invention can be used.

According to the present invention there is provided a fault current circuit breaker comprising a switching mechanism with a fault current tripping device, which device comprises a yoke body made up of layers of a ferro-magnetic material extending in parallel and separated by a non-ferromagnetic material or air, a permanent magnet and a tripping armature bridging the layers of the yoke body, which yoke body comprises an opening arranged so that at the area where the tripping armature bears against the yoke body the cross sectional area of the latter is reduced for the magnetic flux which is continuous and without an air gap in the layers around the opening, characterised by the fact that the main current paths of the fault current circuit breaker are guided through the opening in the yoke body of the fault current tripping device.

The present invention enables tripping to be achieved with D.C.fault currents which increase slowly as it can be seen that instead of using a summation transformer the main current paths of the fault current circuit breaker are guided directly through the opening in the yoke body of the fault current tripping device.

The yoke body then acts so to speak as a summation transformer.

This naturally causes constructional problems in order to achieve symmetry. Problems of heating and insulating strength also needing to be solved, because the opening in the yoke body must be as small as possible. Since there is no possibility of adapting the excitation circuit to the value of the exciting fault current, high requirements are also made of the sensitivity of the tripping device. However, all these difficulties can be overcome with modern materials and modern technology. On the other hand, the losses in the summation transformer are consequently eliminated and due to the saving of the transformer, the present invention provides not only economical advantages, but also a possible reduction in the dimensions of the appliances, which proves particularly important for example in a combination of a fault current circuit breaker with a wall socket.

In order to use the space available in the yoke window in an optimum manner, the main current paths of the fault current circuit breaker are preferably adapted to the shape of the yoke window, at the point at which they are guided through the yoke window. With a quadratic or rectangular opening, quadratic or rectangular cross sectional shapes represent the most favourable solution and with a circular opening, cross sectional shapes of the main current paths in the shapes of the main current paths in the shape of a segment of a circle represent the most favourable solution.

The present invention will now be described by way of example with reference to the accompanying drawing, in which: Figure 1 is a circuit diagram incorporating a fault current circuit breaker according to the present invention; and Figures 2 and 3 are diagrams showing two examples of the adaption of the cross sectional shapes of the main current paths to the shape of a yoke window of a fault current circuit breaker as shown in Fig. 1.

As shown in Fig. 1, the fault current circuit breaker comprises a fault current tripping device 1 which comprises a permanent magnet 2 and a tripping armature 3 bridging a yoke body 4. The yoke body 4 comprises a plurality of layers of a ferromagnetic material which layers extend parallel to one another and are separated by layers of a non-ferromagnetic material on air. The main current paths L1, L2, L3 and N are guided as continuous turns through a yoke window 4A in the yoke body 4.

The trimming armature 3 actuates a switching mechanism 5, which in turn actuates the contact mechanism 6, a testing circuit.7 and connecting terminals 8 in known manner.

Figs. 2 and 3 show variations in the cross sectional shape of the yoke window 4A and the adaptation of the cross-sectional shapes of the main current paths to the shape of the yoke window 4A. In Fig. 2, the yoke window 4A is of circular cross section and the four main current paths shown make up four equal circular segments to fill this cross sectional shape whereas in Fig. 3 the yoke window is of square cross section and the four main current paths shown are each of square cross sectional area occupying a quadrant of the square cross sectional area of the window 4A.

Claims

1. A fault current circuit breaker compriing a switching mechanism with a fault current tripping device, which device comprises a yoke body made up of layers of a ferromagnetic material extending in parallel and separated by a non-ferromagnetic material or air, a permanent magnet and a tripping armature bridging the layers of the yoke body, which yoke body comprises an opening arranged so that at the area where the tripping armature bears against the yoke body the cross sectional area of the latter is reduced for the magnetic flux which is continuous and without an air gap in the layers around the opening, characterised by the fact that the main current paths of the fault current circuit breaker are guided through the opening in the yoke body of the fault current tripping device.

2. A fault current circuit breaker as claimed in claim 1, in which the portions of the main current paths which are guided through the opening of the yoke body are adapted in shape to the cross sectional shape of the opening.

3. A fault current circuit breaker substantially as hereinbefore described with reference to Figs. 1 and 2 or Figs. 1 and 3 of the accompanying drawing.